To master the incipient motion of newly deposited fine sediment under different saline conditions，we carry out three series of mud incipient tests with circulating flume，including salt-free mud incipient motion tests in saltwater（saltwater-salt-free mud），salt mud incipient motion tests in saltwater（saltwater-salt mud），and salt mud incipient motion tests in freshwater（freshwater-salt mud）. On the basis of the particle image velocimetry（PIV）system and digital image gray processing technology，we identify quantitatively the critical incipient velocity of sediment. The results show that the higher salinity of water body or cohesive sediments makes it more difficult to start. There is a logarithmic relationship between the incipient velocity of cohesive sediments and the salinity of water or cohesive sediments. The incipient velocity increases sharply at the salinity of 0‰-10‰ and slowly at the salinity of 10‰-40‰. For the same salinity，the incipient velocity of salt mud in freshwater is the highest，followed by that of salt mud in saltwater，and that of salt-free mud in saltwater is the lowest. For sandy silt mixtures containing gravel，it is easy to flocculate in saltwater. However，the flocs are easy to disperse under high-speed stirring at 520 r/min，so salinity has little effect on the incipient motion of sandy silt.